1. Field of the Invention
The present invention generally relates to operation of a remote plasma unit connected to a semiconductor-processing apparatus, and particularly to a method of maintaining the remote plasma unit.
2. Description of the Related Art
Chemical Vapor Deposition (CVD) is a processing method widely used in the semiconductor industry. In a CVD process, a thin film is formed on a semiconductor wafer substrate by causing a chemical reaction of various gases in a process container. There is a method of generating gaseous plasma during a deposition process to allow thin film deposition on the substrate at a lower temperature and at a higher deposition rate in the process container. This type of process is called a Plasma-Enhanced CVD (PECVD) process.
A thin film is also deposited on a wall surface of the process container and on other parts during deposition processing and particles are generated. If these particles adhere to the substrate, considerable damage is caused in a minute semiconductor-processing process; hence such contamination particles must be removed.
Consequently, in a PECVD process, it is necessary to remove film accumulation resulted from a previous process by regularly cleaning the process container. Cleaning processing is achieved normally by introducing a fluorinated gas such as NF3 into the process container.
In the cleaning processing as well, plasma is generated in order to remove film accumulation efficiently. Hitherto, as shown in FIG. 1, an In-Situ cleaning method in which plasma 4 is generated using parallel flat-plate type electrodes (an upper electrode 2 and a lower electrode 3) disposed in a process container 1 was used. In recent years, however, remote plasma cleaning went into wide use for the following reasons: (1) Less electrode damage is caused because ion bombardment is not developed in the process container; (2) cleaning of portions other than the electrodes is possible; (3) dissociation efficiency is high because large-amount power input is possible.
More specifically, as shown in FIG. 2, the remote plasma cleaning is a cleaning method in which a plasma is generated in a remote plasma unit (RPU) 5 provided outside the process container 1, F radicals 6 are generated by decomposing a fluorinated gas by the plasma, and cleaning is performed by introducing the F radicals generated into the process container.